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-   -   Solving simeltaneous equations using matrices (https://www.askmehelpdesk.com/showthread.php?t=202507)

  • Apr 5, 2008, 09:01 AM
    confusedbuzz
    Solving simeltaneous equations using matrices
    How can you solve a pair of equations with 2 variables if you've been given a matrix with the variables?
    Like suppose you're given

    (4 -1 )
    (-3 2 )

    and the two equations given are

    y = 4x + 8
    2y -3x + 1 = 0
  • Apr 5, 2008, 09:05 AM
    ISneezeFunny
    Confused, I'm not sure if it's because I'm hung over... but to me, that question doesn't make sense.

    in the matrix, is x = (4, -3) and y = (-1, 2)? If that's the case, then that doesn't work within the equations.

    You can solve the equation below even without the matrix as

    y = 4x + 8

    substitute
    2(4x + 8) - 3x + 1 = 0
    5x + 17 = 0
    5x = -17
    x = -17/5

    not entire sure what the matrix has anything to do with it.
  • Apr 5, 2008, 09:47 AM
    confusedbuzz
    Yeah exactly. I knew how to solve it using elimination or substitution but the question gives the matrix and says to use it.

    (4 -1 )
    (-3 2 )

    y = 4x + 8
    2y -3x + 1 = 0

    If you see the first term in the matrix (4), it is the x coefficient in the first equation. The second term (-1) can be the y coefficient [if you move it to the other side of the = sign].

    The third term (-3) is the coefficient of x in the second equation and the fourth term (2) is the coefficient of y in the second equation.


    AHHHHH I don't know :S
  • Apr 5, 2008, 10:09 AM
    ISneezeFunny
    OK OK I got it.

    sorry. Had to "recover" for a bit...

    if you change the two equations so that they have a constant on each side:
    4x - 1 = -8
    -3x + 2y = -1

    then you can make a matrix

    ( 4 -1) (x) = (-8)
    ( -3 2) (y) = (-1)

    then you find the inverse of the 2x2 matrix and left multiply to the (-8, -1)
  • Apr 5, 2008, 10:16 AM
    confusedbuzz
    Haha oh okay I get it now
    Thanks a lot!
    Sorry I can't rate its not letting me but ill be sure to do it asap

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